Active antenna arrays are increasingly required for sensors, communications, and electronic warfare systems. Active antenna arrays are arrays of antenna elements in which each antenna element or subset of antenna elements is driven by, or drives, one or more active radio-frequency (RF) device(s) such as a monolithic microwave integrated circuit (MMIC). Some prior art arrangements associate a transmit-receive (TR) module with each antenna element, as described in U.S. Pat. No. 5,017,927, issued May 21, 1991 in the name of Agrawal et al. or with a subset of antenna elements of the array, as described in U.S. Pat. No. 5,339,086, issued Aug. 16, 1994 in the name of DeLuca et al. Active array antennas are advantageous in that their beams can be steered instantaneously by simply adjusting the relative phase shifts of the signals to each antenna element or subset. They have the disadvantage, in general, of being expensive by comparison with antenna types such as reflector antennas.
At one time, the cost of the microwave monolithic integrated circuit (MMIC) was a major cost obstacle, and other costs, such as the TR module and antenna structure, were secondary. The art of making MMICs has improved, and their cost has decreased to a point at which the cost of the TR module structure and the antenna array structure have become important relative cost factors. Improved TR module arrangements for active antenna arrays are desired.